WEBOctober 31, 2023. (2023-10-31) (aged 76) Tokyo, Japan. Alma mater. Keio University. Koichi Yamamoto (山本 公一, Yamamoto Kōichi, September 4, 1947 – October 31, 2023) was a Japanese politician of the Liberal Democratic Party, a member of the House of Representatives in the Diet (national legislature).